JPS5923579A - Green color light emitting diode and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use Visible light emitting diodes (LEDs) are widely used as pilot lamps and as display elements such as numeric display elements and level indicators. Especially red in the field of displays.

Three-color LEDs, yellow and green, are often used and are formed by sequentially growing n-type and p-type epitaxial layers on a gallium phosphide (GaP) substrate.
Along with red LEDs, they occupy a central position among visible LEDs. The present invention provides GaP suitable for the above-mentioned display element.
Regarding green LED.

;Conventional structure and problems GaP green LEDs contain nitrogen (N) as the emission center6
There are two types: a yellow-green LED with a peak emission wavelength at 66 nm and a pure green LED that does not contain nitrogen and has a peak emission wavelength at 656 nm. Both of these structures are n-type G
It is formed by sequentially growing n-type and p-type epitaxial layers on an aP substrate.

GaP substrates are generally slimmed in the <111> direction, and have an A-plane (gallium surface) and a 3-plane (burnt surface).
There is. Side A is chemically stable and resistant to etching.
If an epitaxial layer is formed on the A-plane of the 8-plane, the epitaxial layer is still difficult to be doped with impurities, so the epitaxial layer is usually grown on the 8-plane. The n-type surface of the GaPLED thus formed is the A-plane.

Figure 1 shows a conventional GaP green LE with such a structure.
FIG. 2 is a diagram showing a cross-sectional structure of a portion D, in which an n-type GaP epitaxial layer 2 is grown on an n-type GaP substrate 1, a p-type GaP epitaxial layer 3 is grown on this, and electrodes 4 and 6 are grown. It has a structure in which the GaP green LED element formed by providing the LED element is fixed to a support 6 such as a stem. By the way, as mentioned above, 8 of the GaP substrate 1
An epitaxial layer is formed on the surface, while Ga
The A surface, which is the n-type surface of the P green LED, is polished to a mirror surface in order to make the thickness of the GaP substrate 1 uniform and to increase the light reflectance on this surface. And Ga
In the P green LED, the light emitted near the pn junction and emitted to the outside consists of a light component that is emitted directly to the outside, as shown by X in the figure, and a light component that is emitted directly to the outside, as shown by Y in the figure, as shown in the figure.
It is roughly divided into light components that are once reflected on the A surface and emitted to the outside.

The light emission of the GaP green LED is close to the band gap of GaP and has strong internal absorption. Therefore, most of the light that is multiplely reflected within the GaP green LED is absorbed,
Further, as described above, the absorption of the light component Y, which is once reflected by the A plane and emitted to the outside, is also large.

For this reason, it has not been possible to obtain high light emission output with the conventional G a P green LED.

Such a problem also occurred in the G a P yellow-green LED.

Purpose of the Invention The present invention reduces the amount of light emitted inside a GaP green LED by internal absorption of the light component emitted to the outside through internal reflection, thereby producing a GaP green LED with high luminous output.
It is an object of the present invention to provide an ED and a method for manufacturing the same.

Structure of the Invention The present invention provides GaP as a starting material for a GaP green LED.
When the A-side of a P substrate, which is difficult to etch, is etched with aqua regia, etch pits and hexagonal irregularities due to crystal defects are generated on the etched surface. This was done based on the confirmation that uneven processing could be applied, and the structure of the GaP green LED was changed to a GaP green LED.
An n-type gallium phosphide epitaxial layer is formed on an n-type gallium phosphide substrate, which is a starting material for ED, and a p-type gallium phosphide epitaxial layer is further formed on the n-type gallium phosphide epitaxial layer. The manufacturing method for obtaining this structure is to create a structure in which the n-type surface opposite to the epitaxial layer formation surface is textured.
After forming n-type and p-type gallium phosphide epitaxial layers on an n-type gallium phosphide substrate prepared as a starting material for a P-green LED, the epitaxial layer is formed on the n-type gallium phosphide substrate on the opposite side of the epitaxial layer formation side. The method is characterized in that the n-type surface of the substrate is etched with aqua regia to make the n-type surface uneven. In a GaP green LED whose n-type surface (A-side) is made to have a textured surface using this method, the reflection of light emitted internally on the n-type surface becomes diffuse reflection, and is reflected externally from the side of the GaP green LED element. Light is emitted, the amount of light absorbed is reduced overall, and high light output is obtained.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 is a sectional view showing an embodiment of the GaP green LED of the present invention, and its basic structure is the same as the conventional one shown in FIG.

However, as shown in the figure, the n-type surface (A-side), which is the surface of the GaP green LED element that is bonded to the support 6,
has an uneven surface, so of the light emitted inside,
The light reflected by the n-type surface is diffusely reflected by the unevenness. In other words, the light reflected by the n-type surface is p
It is divided into a light component Y emitted to the outside from the mold surface (one surface) and a light component Z emitted to the outside from the side surface, and most of it is occupied by the light component 2. The passage distance inside the element of the light component Z emitted to the outside from this side surface is shorter than that of the light component Y, and therefore the amount of internal absorption is reduced. In other words, out of the light components reflected by the n-type surface (A-plane), the amount of light emitted to the outside of the element increases, and the Ga
The light emitting output characteristics of the P-green LED are improved compared to the conventional structure.

By the way, the GaP green LED of the present invention having such a structure is formed by the method described below. First, n-type and p-type epitaxial layers are sequentially grown in a liquid layer on an n-type GaP substrate. Next, the n-type side of the epitaxially grown GaP substrate is removed by polishing to a predetermined thickness, and then only the polished surface is exposed and etched with aqua regia for several minutes. Through this etching process, the n-type surface (
Side A) becomes an uneven surface as shown in Fig. 2, and after this, electrodes are formed and the element is adhered to the support, and a G a P green light LED with the structure shown in Fig. 2 is formed. be done.

FIG. 3 shows n to confirm the effect of the present invention explained above.
Compare the light emitting output of a GaP pure green LED with a conventional structure formed by mirror polishing the mold surface and a GaP pure green LED of the present invention whose n-type surface is formed by etching with aqua regia to create unevenness. FIG.

As shown in the figure, according to the structure of the present invention, the light emission output is approximately 20 times larger than that of the conventional structure, and a high light emission output is achieved.

Note that similar results were obtained when the present invention was applied to a GaP yellow-green LED.

Effects of the Invention According to the present invention, it is possible to increase the light emitting output of a GaP green LED without making any major changes to the basic structure or four basic manufacturing steps of the GaP green LED. This has the effect of expanding the scope of application to the display field.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the structure of a conventional GaP green light LED whose n-type surface is mirror-polished, and Fig. 2 is a GaP green LED of the present invention whose n-type surface is made uneven by aqua regia etching.
Figure 3 is a cross-sectional view showing the structure of a conventional GaP pure green LE.
FIG. 4 is a diagram showing a comparison of the light emission outputs of the G a P pure green LED of the present invention and the G a P pure green LED of the present invention. 1...n-type GaP substrate, 2...n-type G
aP epitaxial layer, 3... p-type GaP epitaxial layer, 4... n-type surface side electrode, 6...
... p-type surface side electrode, 6 ... support body (stem)
. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure m2 Figure 3

Claims (1)

[Scope of Claims] (1) An n-type gallium phosphide epitaxial layer is formed on an n-type gallium phosphide substrate, and further, a p-type gallium phosphide epitaxial layer is formed on the n-type gallium phosphide epitaxial layer, and
A green light-emitting diode characterized in that the n-type surface of the gallium phosphide substrate, which is opposite to the surface on which the epitaxial layer is formed, is textured. (2) After forming n-type and p-type gallium phosphide epitaxial layers on an n-type gallium phosphide substrate, the n-type surface opposite to the epitaxial layer formation side of the n-type gallium phosphide substrate is coated with aqua regia. 1. A method for manufacturing a green light emitting diode, which comprises etching the n-type surface to have an uneven surface.